Patients that suffer from stroke, cardiac arrest, or trauma, such as head trauma, as well as patients that have undergone invasive brain or vascular surgery, are at risk for ischemic injury. Ischemic injury occurs as a result of a lack of oxygen (e.g. lack of oxygenated blood) to an organ, such as caused by a blockage or constriction to a vessel carrying blood to the organ. For example, in the case where a patient suffers a heart attack, typically, a clot can block one of the coronary arteries that carries blood and oxygen to the patient's heart muscle. As a result of the blockage (e.g., an ischemic condition) the patient's heart can experience ischemic tissue injury or heart damage. In the case where a patient suffers from a stroke, typically, a clot blocks the blood supply to a portion of the patient's brain. The blockage, in turn, causes ischemic damage to the brain tissue. For example, as a result of the stroke, the brain experiences a critical or terminal rise in intra-cranial pressure, brain cell death, and a loss of brain function.
Induction of systemic hypothermia (e.g., a hypothermic state) in a patient may minimize ischemic injury when the patient suffers from a stroke, cardiac arrest, heart attack, trauma, or surgery. For example, in the case where the patient suffers a heart attack, the effectiveness of hypothermia is a function of the depth (e.g., within a temperature range between approximately 30° C. and 35° C. for example) and duration of the hypothermic state as applied to the heart. The effectiveness of the hypothermia is also a function of the amount of time that elapses between the original insult (e.g., heart attack) and achievement of protective levels of hypothermia. Also, for trauma and stroke patients, hypothermia aids in controlling swelling of the patient's brain. Furthermore, surgeons typically use hypothermia during brain and other invasive surgeries to protect the brain from surgical interruptions in blood flow.
Systemic hypothermia has historically been applied, such as by immersion of the patient's body in a cool bath, where the depth and duration of hypothermia is limited by the patient's ability to tolerate the therapy. Currently, there are several conventional systemic hypothermia systems available. Such conventional systems include blankets or pads where cooled water is circulated through channels in the walls of the blanket or pad and the patient's body contacts the walls of the blanket.
Attempts have been also made to induce hypothermia in a patient by local cooling the surface of the patient's head. For example, a conventional head-cooling device involves a head cap with a gel substance contained within the walls of the cap. Prior to use, for example, a user (e.g., medical technician) places the head-cooling device in a freezer to reduce the temperature of the gel within the cap. During operation, the user fits the reduced-temperature cap to the head of a patient. The gel within the walls of the cap absorbs heat from the head, thereby cooling the head of the patient.
Other conventional devices induce systemic hypothermia in a patient by providing contact between a tissue region of interest and a cooling fluid. For example, one conventional device includes a flexible hood having multiple ribs or studs disposed on the inner surface of the hood. When a user places the hood on a head of a patient, the ribs or studs contact the head and maintain a fluid circulation space between the head and the hood and an edge, defined by the hood, contacts the patient's skin. A negative pressure source draws a cooling fluid through the flexible hood, under negative pressure, to cause the fluid to contact the scalp of the patient and draw heat away from (e.g., cool) the scalp. Furthermore, application of the negative pressure seals the edges of the hood against the skin of the patient (e.g., a region substantially free of hair).